Five RCB stars – HD 175893, ASAS-RCB-11, IRAS 18135.5-2419, WX CrA and EROS2-CG-RCB-6 – have prominent \(^{12}\) C\(^{18}\) O absorption features and are consistent with \(^{16}\) O/\(^{18}\) O \(< 1\) . We derive \(^{16}\) O/\(^{18}\) O values of 0.01–0.2, 0.01–0.2, 0.5–5, 0.05–0.5 and 0.2–5 for these stars respectively. These values are similar to those of dLHdC stars. We note that our derived \(^{16}\) O/\(^{18}\) O values for HD 175893, S Aps, SV Sge, ES Aql, U Aqr, Z Umi and WX Cra agree with previous medium resolution measurements from [1]}. Our derived values also agree with high resolution measurements for all of these except S Aps, SV Sge and ES Aql, as the \(^{12}\) C\(^{16}\) O bandheads are saturated in these three [2]}. Finally, the RCB star EROS2-CG-RCB-4 shows the \(^{13}\) C\(^{16}\) O absorption bandhead at 2.345, 2.374, 2.404 and 2.434 \(\) m (see Figure REF ).
